design for a 6-8cuft box between30-34hz

i got 2 db drive k715d4's i wanna put in a 6-8 cuft box tuned to between 30 and 34hz to go into the back of my 2004 chevy trailblazer. i dont know which would be louder between band pass or ported but i dont want it to just be sealed. is there a cost for the design?? i can fold the 3rdrow seating down as well cuz ill never need it but it doesnt lay flat when folded down it leaves about a 4to 5 inch lip. let me know if u need more pics or full out measurements.